The applicants proposed that noninvasive thermal imaging will be required to resolve clinical hyperthermia dosimetry questions at a quantitative level. They further hypothesized that incident microwave illumination of the treatment volume of interest can be used to image temperature dependent tissue electrical properties from which thermal images can be extracted. Microwave imaging of biological tissue has long been regarded as a potentially powerful imaging modality which has been limited in the past by the complexities associated with image reconstruction and data acquisition. They proposed that they have overcome many of these difficulties to the extent that in vivo microwave imaging can become a practical reality with direct application to the noninvasive thermal imaging problem associated with hyperthermia cancer treatment. To achieve the overriding goal of demonstrating proof-of-concept thermal images in vivo with microwave illumination, the applicants proposed a research plan having the specific aims of (1) constructing a 64 channel data acquisition system, (2) developing an illumination chamber concept for in vivo use which can be easily interchanged with the data acquisition hardware, (3) advancing imaging reconstruction software to include, among other capabilities, 3-D volumetric image formation and (4) quantifying prototype system performance for anatomical and thermal imaging using in vitro and in vivo models. If successful with these aims, the applicants projected to be able to enter into a human subjects feasibility trial where they would hope to demonstrate that microwave thermal imaging can provide the type of treatment assessment information that is required to advance current concepts of hyperthermia dose measures in terms of their value in predicting treatment outcome.